RU2565703C2 - Mould, method of mould production and method of production of article from plastic or composite material with help of this mould - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention discloses the induction-heated mould including at least one lower part and one upper part to confine the cavity. Moulding material is loaded into the mould, heated to temperature Ttr higher than 20°C and moulded therein. Note here that at least one of mould parts includes the zone of heat transfer with forming material. Heat transfer zone includes at least one subzone of heat transfer made of at least one ferromagnetic material with Curie point Tc varying from 20 to 800°C to contact with forming material and/or with non-ferromagnetic coating with specific heat conductivity of 30 W·m^-1·K^-1.Besides, invention covers the mould production process and method of article production from plastic or composite material.

EFFECT: simplified production of mould and its design, ease of modulation of unknown magnetic and/or thermal characteristics.

23 cl, 1 dwg, 7 ex

Description

The present invention relates to a form intended, in particular, for the manufacture of articles of plastic or composite material, although this scope is not intended to limit the invention.

It is known that it is most preferable to apply the molding method using electromagnetic induction heating, in particular with the aim of quickly and efficiently heating plastic or composite materials intended for molding, as well as for heating parts of metals or metal alloys before they are stamped and quenched in a stamp.

With this method of induction heating, the molding device contains inductors through which a medium-frequency current I _{gen is} passed, generated by a power generator and generating an electromagnetic field that varies in time. This alternating field underlies the well-known phenomenon of electromagnetic induction: when applied to a current-conducting material, it creates a time-varying magnetic flux and voltage induced in the conductive material, which in turn creates induced currents on the surface of the conductive metal at a depth , called the thickness of the surface layer δ and determined by the ratio

, $$\delta =\sqrt{\frac{2}{\mu \cdot \sigma \cdot \omega }}$$

,

, σ обозначает удельную электрическую проводимость материала (величина, обратная удельному электрическому сопротивлению Rel), ω обозначает круговую частоту и равно $$2\cdot \pi \cdot f$$

, где f является частотой тока возбуждения и генерируемого магнитного поля.in which µ denotes the magnetic permeability of the material at

, σ denotes the electrical conductivity of the material (the reciprocal of the electrical resistivity Rel), ω denotes the circular frequency and is equal to $$2\cdot \pi \cdot f$$

where f is the frequency of the excitation current and the generated magnetic field.

If the conductive material is not a ferromagnet, the value of µ _{r is} close to 1, and the thickness of the surface layer is determined by the ratio

$${\delta }_{amagn}=500\sqrt{\frac{\mathrm{Re}l}{f}}$$

In this regard, there is a known method of induction heating of material from document FR 2867939, which describes a form that allows you to place in the cavity of the source material, which acquires its final properties after heat treatment. Passing an electric current of medium frequency through the inductor leads to the appearance of induced currents in the thickness of the surface layer of the intermediate part in contact with the heated material, which limits the volume of mold parts that need to be heated.

In addition, plug-in blocks made of materials with different values of electrical resistivity or magnetic permeability can be arranged inside this intermediate element in order to achieve different surface temperatures.

However, the inventors have found that sizing and inserting plug-in units into a mold is a complex operation that does not allow very precise control of surface temperatures.

In addition, even if this installation is carried out very accurately, which will take considerable time, it is noted that some surface areas undergo overheating or insufficient heating, which adversely affect the formation of the product, for example, leading to an uneven distribution of hardness.

In addition, whatever the geometry of these parts, temperature fluctuations are observed at the level of the heat transfer zones, further exacerbating the aforementioned phenomena of overheating or insufficient heating.

The present invention is intended to eliminate these drawbacks and to do this, propose a form that is easier to manufacture, allowing to smooth the heterogeneity of the molding temperature, and also propose a method of manufacturing such a form, which makes it easy to modulate the desired magnetic and / or thermal characteristics.

In this regard, the first object of the invention is a mold containing at least one lower part and one upper part defining a cavity into which the material to be molded is loaded, heated to a temperature Ttr above 20 ° C, which is then molded by contact with these lower and upper parts of the mold, heated by the induced current generated by at least one electromagnetic inductor, while at least one of these lower and upper parts contains a zone of heat transfer with said moldable material, wherein said heat transfer zone comprises at least one heat transfer subzone made of at least one ferromagnetic material with a Curie point Tc in the range of 20 to 800 ° C that comes into contact with the moldable material or with a coating of non-ferromagnetic material with a specific thermal conductivity exceeding 30 W · m ^-1 · K ^-1 , which, in turn, comes into contact with the specified molded material.

In the framework of the present invention, a heat transfer zone is understood to mean a zone or zones of the form through which an induced current generated by an electromagnetic inductor passes. As mentioned above, the thickness of this zone depends on the average specific resistance of the mold material and on the frequency f of the excitation current and in any case does not exceed δ _amagn .

Preferably, this heat transfer zone is monoblock, that is, it is a massive zone, which is made in the form of a single unit, and not in the form of a set of elements, and which cannot be disassembled. However, this term does not exclude the presence of one or more coatings combined with the base substrate.

In a preferred embodiment, said heat transfer zone comprises at least two heat transfer subbands characterized by magnetic permeability near said temperature Ttr, wherein at least one of said subbands is made of a ferromagnetic material with a Curie point Tc from 20 to 800 ° C, each of these subzones comes into contact with the specified molded material and / or with a possible coating made of non-ferromagnetic material with a specific thermal conductivity of more than 30 W · m ^-1 · K ^-1 , which, in turn, comes into contact with the specified moldable material.

In an alternative version of this preferred embodiment, the heat transfer subbands have identical Curie points, but are made using different amounts of magnetic compounds.

In another version of this preferred embodiment of the form related to the second aspect of the invention, the heat transfer subbands have different Curie points and can be made of two iron-nickel alloys of different composition or of an iron-nickel alloy of the same composition, but with different crystallographic structure.

In addition, the forms in accordance with the invention may have the following distinctive features, taken separately or in combination:

- the cavity contains at least one angular zone, and this zone covers at least one heat transfer subzone,

- the coating of non-ferromagnetic material is made of aluminum, copper, tin or their alloys,

- the Curie point lies in the range from 60 to 350 ° C,

- the ferromagnetic material consists of an iron-nickel alloy, preferably containing at least 25 wt. % nickel, from 0.001 to 10% manganese, as well as impurities unavoidable in the production and may contain up to 15 wt. % chromium, up to 15 wt. % cobalt, up to 15 wt. % copper, up to 10 wt. % of at least one element selected from the group consisting of silicon, aluminum, vanadium, molybdenum, tungsten or niobium, and may further comprise at least one element selected from the group consisting of sulfur, boron, magnesium or calcium .

The second object of the invention is a method of manufacturing a mold according to the first object of the present invention, according to which the upper part and the lower part of the mold are defined, which define a cavity, at least one of said upper and lower parts contains a heat transfer zone containing a ferromagnetic metal alloy, then a layer non-ferromagnetic material with a thermal conductivity greater than 30 W · m ^-1 · K ^-1, for all or part of the portion of said heat transfer area made of said ferromagnetic alloy. Preferably, the metal or metal alloy layer with a thermal conductivity exceeding 30 W · m ⁻¹ · K ⁻¹ consists of aluminum, copper, tin or their alloys, in particular copper and nickel alloys.

A third object of the invention is a method for manufacturing a mold according to a second aspect of the invention, according to which an upper part and a lower part of a mold defining a cavity are prepared, wherein at least one of said lower and upper parts comprises a heat transfer zone containing a ferromagnetic metal alloy, and then a non-ferromagnetic layer is applied metal or alloy for the whole or part of a portion of said heat transfer zone made of said ferromagnetic alloy, and said metal layer is diffused Whether the alloy by local heat treatment, said metal or alloy is selected so as to cause precipitation of nonmagnetic phases due to its diffusion, thereby forming the heat transfer subband, the number of magnetic compounds wherein differ completely or partially from the remainder of the heat transfer area. Preferably, the heat transfer zone initially comprises an austenitic, or austenitic-ferritic, or austenitic-martensitic iron-nickel alloy, which contains at least 25 wt. % nickel, from 0.001 to 10% manganese, as well as impurities unavoidable in the production and which may contain up to 15 wt. % chromium, up to 15 wt. % cobalt, up to 15 wt. % copper, up to 10 wt. % of at least one element selected from the group consisting of silicon, aluminum, vanadium, molybdenum, tungsten or niobium, and may further comprise at least one element selected from the group consisting of sulfur, boron, magnesium or calcium and the non-ferromagnetic metal is aluminum.

A fourth aspect of the invention is a method of manufacturing a mold according to a second aspect of the invention, according to which an upper part and a lower part of a mold defining a cavity are prepared, wherein at least one of said lower and upper parts comprises a heat transfer zone containing a ferromagnetic metal alloy, then a local thermal processing at least one section of the specified heat transfer zone made of the specified alloy, so as to obtain a heat transfer subzone, crystallog whose afic structure and, therefore, the Curie point differ from all or part of the rest of the heat transfer zone. Preferably, the heat transfer zone initially comprises an austenitic, or austenitic-ferritic, or austenitic-martensitic iron-nickel alloy, which contains at least 25 wt. % nickel, from 0.001 to 10% manganese, as well as impurities unavoidable in the production and which may contain up to 15 wt. % chromium, up to 15 wt. % cobalt, up to 15 wt. % copper, up to 10 wt. % of at least one element selected from the group consisting of silicon, aluminum, vanadium, molybdenum, tungsten or niobium, and may further comprise at least one element selected from the group consisting of sulfur, boron, magnesium or calcium , and said local heat treatment consists in rapidly cooling said portion of the heat transfer zone, which leads to the conversion of all or part of austenite to martensite.

A fifth aspect of the invention is a method for manufacturing a mold according to a second aspect of the invention, wherein an upper portion and a lower portion of a mold defining a cavity are prepared, wherein at least one of said lower and upper portions comprises a heat transfer zone containing a ferromagnetic metal alloy, and then a non-ferromagnetic layer is applied metal or alloy for the whole or part of a portion of the specified heat transfer zone made of the specified ferromagnetic alloy, and diffusion of the specified metal layer Whether the alloy by local heat treatment, said metal or alloy is selected so as to locally change the Curie point by virtue of their diffusion, as well as to receive subband heat, the Curie point is different from all or part of the remainder of the heat zone. Preferably, the heat transfer zone initially contains a nickel-iron alloy that contains at least 25 wt. % nickel, as well as impurities unavoidable in the production and which may contain up to 10 wt. % chromium, up to 10 wt. % cobalt and up to 10 wt. % copper, and said metal deposited at least on a portion of the heat transfer zone is copper.

A sixth aspect of the invention is an induction molding apparatus comprising a mold according to the invention and at least one electromagnetic inductor.

A seventh aspect of the invention is a method for manufacturing an article from a plastic or composite material using the mold of the present invention, according to which said plastic material or said composite materials are loaded into a cavity of said mold, then molding is made by contact with said lower and upper parts of the mold, at least at least one of which is heated to a uniform temperature plus or minus 8 ° C and preferably plus or minus 5 ° C, component from 60 to 350 ° C, due to the action the induced current generated by the specified electromagnetic inductor.

In the framework of the present invention, the term "plastic material" refers to thermoplastic compounds, thermosetting compounds, elastomers, vulcanizable compounds.

In addition, the term "composite material" should be understood as any combination of the aforementioned plastic materials with a substance such as glass, carbon, oxide, metal or a metal alloy. This additional substance can be included in the form of dispersed fibers or in the form of a woven or non-woven mesh, or in the form of one or more panels that adhere to a plastic material to form a sandwich structure or a two-layer structure, or a cellular structure, for example, a honeycomb structure.

It is understood that the determination of the shape in accordance with the invention is based on modulation of the operating characteristics of the heat transfer zone, which makes it possible to reduce the surface temperature heterogeneity of this shape. Indeed, it suddenly turned out that obtaining a uniform temperature on the functional surface of the mold requires a heterogeneity of the working properties of the heat transfer zone.

In particular, it was found that overheating occurs, in particular, in zones of concentration of induced currents, and insufficient heating occurs in areas where induced currents do not circulate. These phenomena depend, in particular, on the geometry of the parts being manufactured, while the corner zones, from sharp angles to right angles, are the site of current concentrations due to the peak effect, while angular zones with obtuse angles are short-circuit zones in which induced current.

In the framework of the present invention, the angular zone should be understood as a zone in which the general direction of the surface of the molding cavity changes significantly.

So, figure 1 presents a sectional view of an example of a known form 1, consisting of two parts, the upper 2 and lower 3, forming in the space between each other a cavity completely filled with plastic material 4 in the molding process. Form 1 is made entirely of magnetic material with a Curie point Tc close to the transformation temperature Ttr of the moldable material. In this case, the manufactured product is a bathtub containing two horizontal side walls 5 and 6 connected to the bottom 7 by two vertical side walls 8 and 9.

The figure also indicates the direction of the magnetic field H, which acts on the shape under the influence of one or more electromagnetic inductors (not shown), through which an electric current of frequency f is passed. Preferably, electromagnetic inductors are integrated in the lower part and in the upper part of the mold body, as shown in FIG. 1 of document FR 2867939. The figure also shows the transmission lines of the induced currents generated by the magnetic field H and shown by two dashed lines in each of parts 2 and 3 forms. Finally, it also shows the zones of the surface layer of parts 2 and 3, limited by dash-dotted lines.

In the case of the presented bath 1, the zones in which significant insufficient heating was observed are located near the zones ab2, bc1, cd1 and ed2, which are also zones in which it is seen that the induced currents pass far from the material during molding, since these currents pass through the shortest path to cross the surface layer zone. These zones can be defined as zones in which the angle from the first part of the bath to the second part is obtuse.

As for the overheating zones, they are observed near the zones ab1, bc2, ed2 and ed1, which are also zones in which it is seen that the induced currents are concentrated due to the peak effect. These zones can be defined as zones in which the angle from the first part of the bath to the second part is acute.

However, if it is necessary to increase the power supplied to a usually insufficiently heated zone, then it turned out that the local zone under consideration must have a magnetic permeability exceeding the magnetic permeability of the surrounding zones in the region of the considered operating temperature, i.e., in the range from + -10 ° C around this operating temperature, which leads to work in heat transfer zones with heterogeneous permeability.

Conversely, if it is necessary to lower the power in a usually superheated zone, the zone under consideration must have a magnetic permeability lower than the magnetic permeability of the surrounding zones at the considered operating temperature, i.e. in the range from + -10 ° C around this working temperature.

Of course, it is preferable to place zones with modified permeability values near the corner zones of the molding cavity, depending on the type of angle being considered. In particular, zones with higher permeability can be located in areas of insufficient heating, and zones with lower permeability in overheating zones in accordance with their definition above.

One of the main variants of the invention relates to obtaining a form containing heat transfer subbands having different values of magnetic permeability, since they are made of magnetic materials with different Curie points.

The control of Curie points can, in particular, be carried out by regulating the composition of the materials under consideration.

It can also be carried out while maintaining a uniform chemical composition, but changing the crystallographic structures of materials depending on the zones under consideration. Indeed, the Curie point of a material is largely dependent on the crystallographic structure and can change dramatically, for example, in the transition from an austenitic structure to a martensitic structure. Such a change in structure is easy to implement, since local heat treatment is sufficient for this, moreover, we can talk about more or less rapid heating (for example, during austenization) and / or more or less rapid cooling.

If the material zone becomes non-magnetic with respect to the other surface zone of the mold, since its temperature exceeds the Curie point lower than the Curie point of the adjacent zone, the permeability of the zone decreases, going from very high values to 1, and the power supplied decreases significantly. At the same time, self-regulation of temperature around the Curie point of the zone with a low Curie point is achieved, which ensures accurate temperature control.

Another variant of the invention is to obtain a form containing heat transfer subbands with different magnetic permeabilities, although they are made of materials with the same Curie points. This local decrease in permeability can, in particular, be achieved by depositing and then precipitating some non-ferromagnetic elements that do not affect the Curie point with the magnetic elements of the initial magnetic alloy so that non-ferromagnetic zones are formed that accordingly lower the permeability of the subzone under consideration.

Iron-nickel alloys are quite suitable for these deposition and diffusion processes, allowing, in particular, to reach conversion temperatures from 60 to 350 ° C, which are fully compatible with the conversion temperatures of most plastic and composite materials, if they contain more than 25 wt. % nickel.

The addition of chromium, cobalt and copper with a content of up to 15 wt. % allows, in particular, to more accurately control the Curie points:

- for example, the Curie point of an austenitic alloy containing 56 wt. % nickel (rest = iron), goes from 530 to 300 ° C, when the percentage of molybdenum is changed from 0 to 11 wt. %;

- for example, the Curie point of an austenitic alloy containing 40 wt. % nickel (rest = iron), goes from 360 to 100 ° C, when the percentage of chromium is changed from 0 to 15 wt. %;

- for example, Curie points of an austenitic alloy containing 30-32 wt. % nickel and 2-8 wt. % chromium (rest = iron) is evenly distributed in the range from -20 to 170 ° C, and for each of these compounds the Curie point can increase by 10-15 ° C for each mass percent of the added element, which are copper or cobalt.

The addition of from 0.01 to 10 wt. % manganese improves the hot forming ability of the alloy.

A preferred alloy in accordance with the invention may additionally contain up to 10 wt. % of at least one element selected from the group consisting of silicon, aluminum, vanadium, molybdenum, tungsten or niobium.

All these elements (Cr, Cu, Co, Mo, Si, Al, Nb, V, W) allow you to adjust the Curie point in different values, although they have different effects on important properties such as electrical resistivity ρel or thermal conductivity δ _th .

So, in austenitic Fe-Ni-Mo alloys, molybdenum significantly increases the electrical resistivity: for example, the electrical resistivity of the Fe-56% Ni alloy increases at ambient temperature from 30 μΩ · cm to 100 μΩ · cm, when the percentage of molydenum increases from 0 up to 9 wt. %

In austenitic Fe-Ni-Cr alloys, chromium significantly increases the electrical resistivity: for example, the electrical resistivity of the Fe-45% Ni alloy increases at ambient temperature from 45 μΩ · cm to 90 μΩ · cm, when the percentage of chromium increases from 0 to 6 wt. %

In austenitic Fe-Ni-Cu alloys, copper significantly reduces the electrical resistivity: for example, the electrical resistivity of the Fe-30% Ni alloy decreases at ambient temperature from 88 μΩ · cm to 78 μΩ · cm, when the percentage of copper changes from 4 to 10 wt. %

Similarly, Si, Al, Nb, V, and W more or less substantially lower the Curie point and increase the electrical resistivity.

Finally, this alloy may further comprise at least one element selected from sulfur, boron, magnesium or calcium. In particular, the total sulfur and boron content is preferably limited to 2 to 60 ppm, while the total magnesium and calcium content is preferably limited to 10 to 500 ppm. These elements allow, in particular, to significantly improve the machinability by cutting for a given alloy grade.

In addition, regardless of the geometry of these parts, temperature fluctuations were also observed at the level of heat transfer zones. Not wanting to be bound by theory, the authors suggested that these oscillations can be associated with the design of inductors, which are made in the form of turns and can be the cause of currents induced “mirror” with respect to their place and their shape.

It was found that these oscillations can be significantly attenuated by covering all or part of the heat transfer zone with a non-ferromagnetic material that conducts heat well. With all obviousness, such a material can perform the function of scattering of thermal waves, which significantly reduces temperature differences. This type of regulation makes sense to apply in non-corner zones, such as zones C1 and C2 of the bathtub shown in FIG.

The thickness of such coatings should usually be less than the thickness of the heat transfer zone and preferably less than one tenth of the thickness of the surface layer.

It goes without saying that the various measurements proposed in the framework of the invention with the aim of homogenizing the surface temperature of the mold can be combined taking into account their compatibility.

Forms in accordance with the invention can be obtained by simple machining of massive blocks of magnetic materials or machining blocks of non-magnetic and even non-metallic materials, after which a layer of magnetic materials is applied using any suitable method, such as plating, plasma deposition, spraying or spraying. In all cases, after obtaining a surface with appropriate geometric dimensions and magnetic properties, you can apply the method of manufacturing the mold in accordance with the invention. This method allows, in particular, simply to obtain a monoblock zone without adding any insert.

To do this, you can use all the options described above, which are used, in particular, for the manufacture of a mold in which at least part of the heat transfer zone contains or even represents an iron-nickel matrix, which is changed in places where it is necessary to ensure good final temperature uniformity .

The following is a more detailed description of the invention, illustrated by non-limiting examples.

Examples

Get a number of forms from different materials, which will be described in each example. All these shapes have the same geometry as the shape shown in FIG. 1 for making a bath.

In the first series of examples, the plastic material for molding the article is a thermoplastic composite material with fiberglass and a polypropylene matrix, which has a conversion point at a temperature of 200 ° C.

In a second series of examples, a plastic material for molding an article is a plastic material with a conversion point at a temperature of 125 ° C.

Unless specifically indicated otherwise, the indicated alloy contents are expressed in mass percent, and all compositions in accordance with the invention contain 0.1% manganese and the usual unavoidable impurities remaining after production.

Comparative Example 1

In order to be able to compare the characteristics of the invention with known solutions, the first molding test was carried out using a mold containing attached metal parts called inserts.

In the previously identified overheating zones, the mold material is locally replaced with these inserts made of non-magnetic materials such as austenitic stainless steel.

The inserts are placed in zones of concentration of induced currents, which allows locally to achieve a large depth of penetration of power. This means that the induced currents no longer concentrate on the extreme surface of the bend, but spread to the surrounding bending zone, thereby dissipating less energy on the bending exchange surface itself.

In this case, it is possible to limit the temperature difference between the mold and the product to an interval of the order of 20-30 ° C, which can be sufficient, but it will require more significant costs for the manufacture of molds, while not providing perfect adjustment and heat transfer of the insert / form, and will not allow some items of complex geometry, such as items in the form of a funnel or a very deep cuvette.

Reference Example 2

After this, a second test of the known solution was made by manufacturing a mold in which the heat transfer zone is made of only one ferromagnetic alloy.

The molds were machined from austenitic FeNi or FeNiCr alloys, known for the ability to easily adjust the Curie point by changing the composition. Indeed, as you know, if you select a Curie point Tc close to a given temperature of the horizontal portion of the curve on the graph (in this case, for molding plastics or composites), you get the phenomenon of self-regulation of temperature around Tc (magnetic and current losses mostly disappear when approaching to the Curie point), and, ultimately, the zones are balanced by insufficient heating and overheating.

With this solution, using an FeNiCr alloy having Tc = 210 ° C, the following is obtained:

- thermal heterogeneity around the apparent angles of the product: ΔT _angle = 15 ° C;

- thermal heterogeneity at the bottom of the bath: ΔT _bottom = 20 ° C;

- thermal heterogeneity due to inductor turns: ΔT _turns = 20 ° C.

Thus, the effect of temperature self-regulation around the Curie point is effective mainly in terms of temperature uniformity in areas with an acute angle, reducing it to 15 ° C, instead of 20-30 ° C in the case of inserts and much larger values in the absence of inserts. On the other hand, there is practically no improvement in other types of thermal heterogeneity.

Example 1

As the starting material, the austenitic alloy FeNiCr is used, the Curie temperature Tc of which is close to 210 ° C - it can be, for example, Fe-35% Ni, or Fe-37% Ni-6% Cr, or Fe-50% Ni-11 , 5% Cr, - in a homogeneous massive state, from which, by machining, a three-dimensional geometric shape of a plastic or composite product is obtained, which is intended for forming by induction heating.

In this example, after machining the heat transfer surfaces, they are covered with a sheet of aluminum foil with a thickness of about 50 μm so that this sheet overlaps the processed functional surface of the mold, that is, both surfaces opposite two mold parts.

Then these two coated mold parts are placed in the furnace, leaving a sheet of aluminum on the upper side of the mold, heat treatment of melting / cladding of aluminum on the surface is applied, heating the mold parts to a temperature of more than 600 ° C for at least several minutes, but allowing only slight diffusion aluminum to FeNiCr alloy. Indeed, the purpose of this heat treatment is only to firmly bond aluminum to the FeNiCr alloy (metal-metal bond).

After this, a molding test is carried out using the mold obtained. At the same time receive:

- thermal heterogeneity around the pronounced angles of the product: ΔT _angle = 12 ° C;

- ΔT _bottom = 20 ° C;

- thermal heterogeneity due to inductor turns: ΔT _turns = 8 ° C.

Thus, the effect of temperature self-regulation around the Curie point is mainly effective in terms of temperature uniformity in areas with an acute angle, and is enhanced by a thin conductive aluminum coating, reducing it to 12 ° C, instead of 15 ° C in the absence of aluminum and 20-30 ° C in the case of inserts, and much larger values in the absence of inserts.

In addition, a thin layer of aluminum plays a very interesting role as a heat dissipator even at such high frequencies and such short intervals of heat transfer time (of the order of a minute), since the thermal inhomogeneity ΔT of the _turns as a result of the direct influence of the localization of the turns of the inductor on the functional surface is brought to 8 ° C , instead of 20 ° C for the absence of aluminum. The temperature of the bottom of the bath remains far from the desired, which in some cases, plastics or technical requirements for the product may be recognized as acceptable.

Example 2

In this example, the conditions of Example 1 are reproduced, but with a different starting alloy, since in this case the goal is to obtain a temperature of 125 ° C in the moldable plastic material during induction heating.

Tests were successively carried out with various FeNiCrCu alloys having a Curie point very close to 125 ° C:

- Fe-32% Ni;

- Fe-30.3% Ni-2% Cr;

- Fe-36.5% Ni-9% Cr-0.2% Mn;

- Fe-29% Ni-2% Cr-3.5% Co;

- Fe-40% Ni-13% Cr-2% Co;

- Fe-30% Ni-2% Cr-3% Cu;

- Fe-28% Ni-2% Cr-5.5% Cu.

Each alloy is supplied in the form of a block, from which, by machining, a three-dimensional geometric shape is made for a plastic material formed by induction heating.

After machining the functional surfaces of the heat transfer, they are covered with a sheet of aluminum foil with a thickness of about 50 μm so that this sheet overlaps the processed functional surface of the mold, that is, both surfaces opposite both parts of the mold. Then these two coated mold parts are placed in a furnace, leaving a sheet of aluminum on the upper side of the mold, heat treatment of melting / cladding of aluminum on the surface is applied, heating the mold parts to a temperature of more than 600 ° C for at least several minutes, but allowing only slight diffusion aluminum to FeNiCr alloy. Indeed, the purpose of this heat treatment is only to firmly bond aluminum to the FeNiCr alloy (metal-metal bond).

After this, a molding test is carried out using the mold obtained. At the same time receive:

- thermal heterogeneity around the apparent angles of the product: ΔT _angle = 10 ° C;

- ΔT _bottom = 16 ° C;

- thermal heterogeneity due to inductor turns: ΔT _turns = 6 ° C.

Thus, they confirm the same advantages in characteristics (reduction of thermal heterogeneity) as in example 1, on the same complex geometry of the product, but at different heating temperatures and with a different initial alloy.

Example 3

In this case, the austenitic alloy Fe-30% Ni-2% Cr-3% Cu, whose Curie temperature Tc is close to 125 ° C, is used to quickly form a plastic material after induction heating.

This alloy is supplied in the form of a block, from which, by machining, a three-dimensional geometric shape is made for a plastic material intended for molding. After machining the functional surfaces of the heat transfer, they are covered with a sheet of aluminum foil with a thickness of 50 μm so that this sheet overlaps the processed functional surface of the mold, that is, both surfaces that are opposite two mold parts.

Then these two coated mold parts are placed in a furnace, leaving a sheet of aluminum on the upper side of the mold, heat treatment of melting / cladding of aluminum on the functional surface is applied, heating the mold parts to a temperature of more than 600 ° C for at least several minutes, but allowing only a slight diffusion of aluminum into FeNiCrCu alloy. Indeed, the purpose of this heat treatment is only to firmly bond aluminum to the FeNiCrCu alloy (metal-metal bond). At this stage, the heat transfer surface corresponds to and is similar to the heat transfer surfaces from the previous examples 1 and 2.

In the next heat treatment step, different from the previous step, some surfaces of the mold are heated by various known means (using a burner, a local inductor, using a pre-heated and contacted metal part, using radiation energy ...) so that the previously clad aluminum diffuses into surface layer, leading to the deposition of a secondary nonmagnetic phase and to a significant decrease in permeability µr.

The sides subjected to this intense surface heating are necessarily sides a1, a2, b1, b2, d1, d2, e1, e2, i.e. all sides of the heat transfer surface except the bottom of the bath (c1 and c2). For deposited aluminum, heating should increase the surface temperature to at least 500 ° C, preferably 600 ° C, so that aluminum diffuses into the surface layer, but too much diffusion of aluminum does not affect the uniformity of the coating.

After this, a molding test is carried out using the mold obtained. At the same time receive:

- thermal heterogeneity around the apparent bends of the product: ΔT _angle = 12 ° C;

-ΔT _bottom = 8 ° C;

- thermal heterogeneity due to the turns of the inductor: ΔT _turns = 11 ° C.

Thus, the effect of temperature self-regulation around the Curie point is mainly effective in terms of temperature uniformity in areas with an acute angle, and is enhanced by a thin conductive aluminum coating, reducing it to 12 ° C, instead of 15 ° C in the absence of aluminum and 20-30 ° C in the case of inserts and much larger values in the absence of inserts. In addition, a thin layer of aluminum plays a very interesting role as a heat dissipator even at such high frequencies and for such short intervals of heat transfer time (of the order of a minute), since the thermal inhomogeneity ΔT of the _turns associated with the direct influence of the localization of the turns of the inductor on the functional surface is brought to 11 ° C, instead of 20 ° C in the absence of a layer of aluminum.

In addition, in the case of forced diffusion of aluminum into the surface layer of some sides of the mold, the temperature of the bottom of the cuvette rises essentially by 8 ° C relative to the desired temperature, which proves the need for temperature control through a calibrated heterogeneity of properties in the heat transfer subzone.

Example 4

In this case, the austenitic and ferromagnetic FeNiCrCu alloy is used at ambient temperature after hot and then cold transformation, followed by recrystallization annealing and cooling at a rate of 5 ° C / h to 5000 ° C / h to ambient temperature, containing from 25 to 36% Ni . Indeed, in this composition range, passing through liquid nitrogen such an austenitic alloy (and, possibly, in some cases, austenitic-ferrite) leads to its complete transformation into martensite, the Curie point of which is much higher than the working molding temperatures provided by the invention (<350 ° C). By localizing this transformation effect under the action of liquid nitrogen in zones of insufficient heating, the temperature of these zones is increased.

Use the heat transfer surface obtained using the alloy of example 3 with a Curie point close to 125 ° C, on the original alloy with one of the following alloys:

- Fe-32% Ni;

- Fe-30.3% Ni-2% Cr;

- Fe-29% Ni-2% Cr-3.5% Co;

- Fe-30% Ni-2% Cr-3% Cu;

- Fe-28% Ni-2% Cr-5.5% Cu,

and then, using the first heat treatment, the aluminum foil sheet is clad on the surface, and then diffusion into the surface layer is carried out using a second heat treatment on sides other than the bottom of the cuvette. Finally, the protruding edges (ab2, bc1, cd1, ed2) of the heat transfer surface, suffering from chronic insufficient heating, are locally treated with nitrogen to obtain a martensitic structure locally and a strong local increase in Tc.

After this, a molding test is carried out using the mold obtained. At the same time receive:

- thermal heterogeneity around the apparent bends of the product: ΔT _angle = 7 ° C;

- ΔT _bottom = 9 ° C;

- thermal heterogeneity due to inductor turns: ΔT _turns = 10 ° C.

In this way, all the advantages already shown in Example 3 are obtained, and an additional significant reduction in the temperature inhomogeneity between the bending zones, which drops to 7 ° C, instead of 10-12 ° C without martensitic transformation.

Example 5

As the starting material, an austenitic or austenitic-ferritic alloy FeNiCr with a content of 25-34% Ni and <11% Cu, the Curie point of which is close to 125 ° C, for example, Fe-28% Ni-5% Cu, is used as the starting material alloy in a massive state, from which, by machining, a three-dimensional geometric shape of the product (plastic or composite) is obtained, intended for molding by induction heating.

After machining the functional surfaces of the heat transfer, they are covered with a sheet of aluminum foil with a thickness of 50 μm so that this sheet overlaps the sides of the processed functional surface of the mold, different from the sides of the bottom of the bath, that is, sides like a, b, d, e, f, g surfaces opposite two form parts. In contrast to the previous examples, the sides of type c (bottom of the cuvette) are covered with a sheet of copper foil 40 μm thick.

Then sequentially carry out the following types of heat treatment:

- melting / cladding of aluminum on the heat transfer surface by heating the mold part to a temperature of more than 600 ° C for at least several minutes, allowing only insignificant diffusion of aluminum in the FeNiCrCu alloy;

- melting / cladding of copper on the heat transfer surface by heating the mold part to a temperature of more than 1000 ° C for at least several minutes, allowing only insignificant diffusion of aluminum in the FeNiCrCu alloy. This treatment is preferably carried out by placing the mold in a furnace, which allows diffusion of aluminum into the surface layer to precipitate secondary non-magnetic phases and control permeability in the corresponding surface layer;

- local surface heating of copper on type c sides, carried out for a sufficiently long time and at high temperature, so that copper mixes with the matrix of the initial FeNiCrCu alloy. Thus, the Curie point on the type c surface is increased.

At the end, the protruding edges of the molding cavity are locally quenched with liquid nitrogen, as described in Example 4, in order to change the microstructure of the magnetic alloy.

After this, a molding test is carried out using the mold obtained. At the same time receive:

- thermal heterogeneity around the apparent bends of the product: ΔT _angle = 6 ° C;

- ΔT _bottom = 8 ° C;

- thermal heterogeneity due to inductor turns: ΔT _turns = 8 ° C.

Thus, using this method, it is possible to achieve a very satisfactory reduction in various thermal inhomogeneities.

It is clear that the present invention has proposed several solutions to minimize the heterogeneity of the surface temperature in the heat transfer zone of the mold, and these various solutions can be arbitrarily combined depending on the specific geometry of the product and, therefore, on the corresponding molding cavity.

The above description relates, in particular, to the molding of plastic material and composite materials, but is not limited to this application, since such a shape can be used to mold other types of materials, such as glass, metals or metal alloys. In the case of the manufacture of metal products, the molding of materials can be carried out, in particular, by hot stamping.

Claims (23)

1. The mold is intended for use in the method of molding with induction heating of the mold, containing at least one lower part and one upper part defining a cavity into which the material intended for molding is loaded, heated to a temperature Ttr exceeding 20 ° C, which then formed by contact with the indicated lower and upper parts of the mold, heated by the induced current generated by at least one electromagnetic inductor, with at least one of these lower and the upper parts comprises a heat transfer zone with said moldable material, wherein said heat transfer zone contains at least one heat transfer subzone made of at least one ferromagnetic material with a Curie point Tc in the range of 20 to 800 ° C that is in contact with the specified moldable material and coated with a non-ferromagnetic material having a specific thermal conductivity exceeding 30 W · m ^-1 · K ^-1 , which, in turn, comes into contact with the specified moldable material. 2. A mold according to claim 1, wherein said heat transfer zone comprises at least two heat transfer subbands characterized by magnetic permeability near said temperature Ttr, wherein at least one of said subbands is made of a ferromagnetic material with a Curie point Tc in the range of 20 up to 800 ° C, with each of these subzones coming into contact with the specified moldable material and with a coating made of non-ferromagnetic material with a specific thermal conductivity exceeding 30 W · m ^-1 · K ^-1 , which, in turn, is included in to ntakt with said moldable material. 3. A mold according to claim 1 or 2, wherein said cavity contains at least one angular zone, wherein at least one heat transfer subzone covers this zone. 4. The mold according to claim 1 or 2, wherein said coating of a non-ferromagnetic material is made of aluminum, copper, tin or their alloys. 5. The mold of claim 1 or 2, wherein said Curie point is in a range of 60 to 350 ° C. 6. The mold according to claim 1 or 2, wherein said ferromagnetic material consists of an iron-nickel alloy. 7. The mold according to claim 6, wherein said ferromagnetic material contains at least 25 wt.% Nickel, from 0.001 to 10% manganese, as well as impurities unavoidable in the production, and may contain up to 15 wt.% Chromium, up to 15 wt. % cobalt, up to 15 wt.% copper, up to 10 wt.% at least one element selected from the group consisting of silicon, aluminum, vanadium, molybdenum, tungsten or niobium, and may additionally contain at least one element, selected from the group consisting of sulfur, boron, magnesium or calcium. 8. The form of claim 2, wherein said heat transfer subbands have identical Curie points, but are made of materials with different contents of magnetic substances. 9. The form of claim 2, wherein said heat transfer subbands have different Curie points. 10. The form of claim 9, wherein said heat transfer subbands are made of two iron-nickel alloys of different compositions. 11. The form of claim 9, wherein said heat transfer subbands are made of an iron-nickel alloy of the same composition, but with a different crystallographic structure. 12. The form according to any one of paragraphs. 1, 2, 8, 9, 10, 11, in which the specified heat transfer zone is monoblock. 13. A method of manufacturing a mold according to one of claims. 1-12, according to which prepare the upper part and the lower part of the form, bounding the cavity, while at least one of these upper and lower parts contains a heat transfer zone containing a ferromagnetic metal alloy having a Curie point in the range from 20 to 800 ° C, then a layer of non-ferromagnetic material with a specific thermal conductivity exceeding 30 W · m ^-1 · K ^-1 is applied to all or part of a portion of the specified heat transfer zone made of the specified ferromagnetic alloy. 14. The method according to p. 13, in which the specified layer of non-ferromagnetic material with a specific thermal conductivity exceeding 30 W · m ^-1 · K ^-1 , consists of aluminum, copper, tin or their alloys, in particular alloys of copper and nickel. 15. A method of manufacturing a mold according to any one of paragraphs. 2-8, according to which the upper part and the lower part of the mold, defining the cavity, are prepared, wherein at least one of the indicated lower and upper parts contains a heat transfer zone containing a ferromagnetic metal alloy, then a layer of the non-ferromagnetic metal or alloy is applied to the whole or to the part a portion of said heat transfer zone made of said ferromagnetic alloy, and diffusing said metal or alloy layer by local heat treatment, wherein said metal or alloy ybirayut so as to cause precipitation of nonmagnetic phases due to its diffusion to form thereby subband heat transfer, the content of magnetic compounds wherein differs from all or part of the remaining heat transfer zone. 16. The method of claim 15, wherein said heat transfer zone initially comprises an austenitic or austenitic-ferritic or austenitic-martensitic iron-nickel alloy that contains at least 25 wt.% Nickel, from 0.001 to 10% manganese, as well as unavoidable in the production of impurities and which may contain up to 15 wt.% chromium, up to 15 wt.% cobalt, up to 15 wt.% copper, up to 10 wt.% at least one element selected from the group consisting of silicon, aluminum, vanadium, molybdenum, tungsten or niobium, and may additionally contain at least e one element selected from the group consisting of sulfur, boron, magnesium or calcium, wherein said non-ferromagnetic metal is aluminum. 17. A method of manufacturing a mold according to any one of paragraphs. 2-7, 9 and 11, according to which the upper part and the lower part of the cavity defining mold are prepared, wherein at least one of said lower and upper parts contains a heat transfer zone containing a ferromagnetic metal alloy, then at least a local heat treatment is performed in the area of the specified heat transfer zone made of the specified alloy, so as to obtain a heat transfer subzone, the crystallographic structure of which and, therefore, the Curie point of which differ from all or part of the core flax heat transfer zone. 18. The method of claim 17, wherein said heat transfer zone initially comprises an austenitic, or austenitic-ferritic, or austenitic-martensitic iron-nickel alloy that contains at least 25 wt.% Nickel, from 0.001 to 10% manganese, as well as unavoidable in the production of impurities and which may contain up to 15 wt.% chromium, up to 15 wt.% cobalt, up to 15 wt.% copper, up to 10 wt.% at least one element selected from the group consisting of silicon, aluminum, vanadium, molybdenum, tungsten or niobium, and may additionally contain at least e one element selected from the group consisting of sulfur, boron, magnesium or calcium, and said local thermal treatment is the rapid cooling of said portion of heat transfer area, which leads to the conversion of all or a portion of the austenite to martensite. 19. A method of manufacturing a mold according to any one of paragraphs. 2-7 and 9-10, according to which the upper part and the lower part of the mold, defining the cavity, are prepared, at least one of the indicated lower and upper parts contains a heat transfer zone containing a ferromagnetic metal alloy, then a layer of a non-ferromagnetic metal or alloy is applied on all or part of a portion of said heat transfer zone made of said ferromagnetic alloy, and diffusion of said layer of non-ferromagnetic metal or alloy is carried out by means of local heat treatment, This metal or alloy is chosen in such a way as to diffuse locally to change the Curie point, thus forming a heat transfer subzone, the Curie point of which differs from all or part of the rest of the heat transfer zone. 20. The method according to p. 19, in which the specified heat transfer zone initially contains an iron-nickel alloy that contains at least 25 wt.% Nickel, as well as impurities that are unavoidable in the production, and which may contain up to 10 wt.% Chromium, up to 10 wt. % cobalt and up to 10 wt.% copper, wherein said metal deposited at least on a portion of the heat transfer zone is copper. 21. A device for molding using induction, containing the form in according to any one of paragraphs. 1-12 or a form that can be obtained using the method according to any one of paragraphs. 13-20, and at least one electromagnetic inductor. 22. A method of manufacturing a product from a plastic or composite material using the mold according to any one of paragraphs. 1-12 or using a form that can be obtained using the method according to any one of paragraphs. 13-20, or by using a molding device according to claim 21, in which said plastic material or said composite materials are loaded into a cavity of said shape, then molding is produced by contacting said lower and upper parts of the mold, at least one of which heated to a uniform temperature within ± 8 ° C, ranging from 60 to 350 ° C, under the action of an induced current generated by the specified electromagnetic inductor. 23. The method according to p. 22, in which the specified temperature is uniform within ± 5 ° C.